If the production of a workpiece necessitates a number of processing sequences, such as cutting and forming, then, for cost-effective production, the necessary individual operations are carried out in a so-called transfer press. The number of tools then corresponds to the number of operating stages which are necessary for producing the workpieces.
The presses contain transporting apparatuses, which transport the workpieces from one work station to the next. The transporting apparatus may be configured as a 2-way transfer means or 3-way transfer means, the movement axes of the transporting means thereby being defined. A 2-way transfer means is provided with supporting rails, which run through the press on both sides. Crossmembers equipped with suction devices or the like are fastened on the supporting-rails for workpiece-transporting purposes The crossmembers execute simultaneous horizontal and vertical movements.
In the case of a 3-way transfer means, the supporting rails are designed as so-called gripper rails, which, in addition to horizontal and vertical movements, also execute a transverse movement and grip the workpiece by means of gripper elements in order to transport the workpiece from one processing stage to the next. The 3-way or gripper-type transfer means is preferably used in practice for transporting flexurally rigid sheet-metal parts which can be gripped from the outside.
Driving action along the 3 axes can take place directly, via cam plates and levers, by means of the press drive, or each movement axis is provided with a dedicated drive. A 3-way transfer means with dedicated drives in each case is disclosed in U.S. Pat. No. 4,887,446. The vertical movement and the closing movement, in the direction transverse to that in which workpieces run through the press, take place by means of electric motors or hydraulic cylinders. An electric linear drive is proposed for executing the horizontal movement of the supporting rails.
No further details are given in U.S. '446 regarding the linear drive and, in particular, there are no further details regarding the lengths of the primary and secondary parts. Similarly, U.S. '446 does not disclose that a gripper-rail change is necessary for retooling purposes.
An arrangement for coupling and uncoupling gripper-rail parts is described in detail in DE 36 36 010. An arrangement based on the principle of a swivel-type tensioning clamp is proposed as the connecting element or gripper-rail lock. In addition to the necessary complex configuration, the task of achieving a clearance between the gripper-rail parts, for the changeover operation, requires considerable outlay.
Instead of the horizontal movement of the supporting rails, this movement can also be produced by virtue of transporting carriages on the supporting rails.